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<p class='vspace'></p><h2>volatile keyword</h2>
<p>volatile is a keyword known as a variable <em>qualifier</em>, it is usually used before the datatype of a variable, to modify the way in which the compiler and subsequent program treats the variable.
</p>
<p class='vspace'></p><p>Declaring a variable volatile is a directive to the compiler. The compiler is software which translates your C/C++ code into  the machine code, which are the real instructions for the LaunchPad.
</p>
<p class='vspace'></p><p>Specifically, it directs the compiler to load the variable from RAM and not from a storage register, which is a temporary memory location where program variables are stored and manipulated. Under certain conditions, the value for a variable stored in registers can be inaccurate.
</p>
<p class='vspace'></p><p>A variable should be declared volatile whenever its value can be changed by something beyond the control of the code section in which it appears, such as a concurrently executing thread. In Energia, the only place that this is likely to occur is in sections of code associated with interrupts, called an interrupt service routine. 
</p>
<p class='vspace'></p><h4>Example</h4>
<pre>
volatile int state = HIGH;
volatile int flag = HIGH;
int count = 0;

void setup()
{
  Serial.begin(9600);

  pinMode(GREEN_LED, OUTPUT);
  digitalWrite(GREEN_LED, state);
  attachInterrupt(PUSH2, blink, FALLING); // Interrupt is fired whenever button is pressed
}

void loop()
{
  digitalWrite(GREEN_LED, state); //LED starts ON
  if(flag) {
    count++;
    Serial.println(count);
    flag = LOW;
  }
}

void blink()
{
  state = !state;
  flag = HIGH;
}

</pre>
<p class='vspace'></p><h4>See also</h4>
<ul><li><a class='wikilink' href='AttachInterrupt.html'>AttachInterrupt</a>
</li></ul><p class='vspace'></p><p><a class='wikilink' href='index.html'>Reference Home</a>
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<p class='vspace'></p><p><em>Corrections, suggestions, and new documentation should be posted to the <a class='urllink' href='http://forum.43oh.com/forum/28-energia/' rel='nofollow'>Forum</a>.</em>
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<p class='vspace'></p><p>The text of the Energia Reference is licensed under a
<a class='urllink' href='http://creativecommons.org/licenses/by-sa/3.0/' rel='nofollow'>Creative Commons Attribution-ShareAlike 3.0 License</a>.  Energia reference is based on Arduino reference.  Code samples in the reference are released into the public domain.
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